The prior art has provided numerous processes for preparing fibrous webs from thermoplastic materials such as polypropylene, polyethylene, polyvinyl alcohol, polylactic acid, and nylons. In many instances, fibrous webs are prepared via weaving of preformed fibers; in other instances, non-woven fibrous webs are prepared via a process such as melt blowing, spun-bonding, and melt-spinning. Innumerable variations of these processes have been provided in the prior art to produce fibrous webs suitable for use in the manufacture of many products.
Some non-woven fibrous webs are useful in the manufacture of clothing. In this regard, it has been known for some time that it is useful to incorporate a temperature stabilizing agent, such as a so-called “phase change material” or “moderate temperature phase change material,” into an article of clothing to provide temperature stabilization. Moderate temperature phase change materials are substances, which undergo a change in phase at a temperature of about 60.degree.-90.degree. F. Because of the well-known thermodynamic principle that a phase change occurs at constant temperature, such materials are useful in preventing heat loss from the body as ambient temperature drops, and conversely, in preventing heat gain to the body as ambient temperature rises. Examples of the use of such moderate temperature phase changes materials are reported in numerous documents, for instance, U.S. Pat. No. 4,856,294, which purports to disclose a vest made with such phase change materials; U.S. Pat. No. 5,366,801, which purports to disclose a fabric containing microcapsules of phase change material; U.S. Pat. No. 5,415,222, which discloses a “micro-climate” cooling garment comprising a vest which contains a “macroencapsulated” phase change material contained within a honeycomb structure, and U.S. Pat. No. 6,120,530, which purports to disclose a passive thermocapacitor for cold water diving garments.
Known moderate temperature phase change materials are conveniently provided in microencapsulated form. The microcapsules of phase change material may be secured to a substrate with the use of a binder, as is purportedly taught in a number of prior patents, including U.S. Pat. Nos. 5,955,188; 6,077,597; and 6,217,993. Alternatively, in the preparation of a fibrous substrate, the microcapsule may be dispersed within a polymeric melt, and fibers may be blown or otherwise prepared from the melt, as is purportedly taught in U.S. Pat. No. 4,756,958. Both of these prior art approaches suffer from a number of drawbacks. Although microcapsules can be secured to a substrate with a binder, this approach is unsatisfactory, because it is believed that microcapsules are susceptible to being debound upon washing or wear of the fabric thus made. Moreover, while in theory these problems are mitigated by incorporating microcapsules into the polymeric melt used to prepare the fibers, it is believed that in practice the microcapsule chemistry is incompatible with the temperatures required to process many thermoplastic polymers. In particular, it is believed difficult to obtain non-woven nylon or polypropylene fabric using such techniques.
It is a general object of the invention to provide, at least in preferred embodiments, a process for incorporating moderate temperature phase change materials into non-woven fibrous webs that is different from the processes heretofore described. In highly preferred embodiments, the invention has as an object to provide nylon and polypropylene non-woven fibrous webs that incorporate microencapsulated materials, and in particular microencapsulated moderate temperature phase change materials.